Powder coatings compositions for use in coating various types of substrates are often desired. Such coating compositions can greatly reduce, or even eliminate, the use of organic solvents that are often used in liquid coating compositions. When a powder coating composition is cured by heating, little if any volatile material is driven into the surrounding environment. This is a significant advantage over liquid coating compositions in which organic solvent is volatized into the surrounding atmosphere when the coating composition is cured by heating.
Powder coating compositions are typically produced by a complex process that includes dry blending various coating components, such as color pigments, film-forming resins, curing agents, and other additives, such as flow control agents and charge control agents, subjecting the resulting blend to heating, melting and kneading by the use of an extruder or the like, and then subjecting the resulting extrudate to cooling, grinding and classification (referred to herein as the “Extrusion Process”). Thus, the Extrusion Process requires many steps.
One disadvantage to the use of powder coating compositions has been that, to obtain various coatings of different hues, the production of a separate powder coating composition for each desired hue has been required. When liquid coating compositions of different hues are mixed, it is possible to obtain a coating having a homogeneous hue that is different from the hue of each mixed liquid coating composition. On the other hand, when typical powder coating compositions of different hues are dry-blended and the resultant blend applied to a substrate, the result is that each hue can be generally distinguished by visual examination with the naked eye, resulting in a “salt and pepper” effect. Thus, it has previously been difficult, if not impossible, to achieve a coating of a desired hue from a dry blend of two or more powder coating compositions of different hues.
As a result, it would also be desirable to provide powder coating compositions suitable for producing a decorative and durable coating having a selected homogeneous hue from a dry blend of two or more powder coating compositions each having a different hue.